The present invention is directed to the isolation of ionic contaminants in planarization fluid compositions and/or removal of ionic contaminants, such as metallic cations, from planarization fluid compositions, e.g., slurries, and methods for using such compositions. More particularly, the present invention is directed to planarization fluid compositions exposed to, i.e., pre-treated, or containing one or more macrocyclic polyethers or xe2x80x9ccrownxe2x80x9d ethers that selectively chelate ions of a specific size.
A large fraction of yield losses in wafer fabrication or processing of semiconductor devices is attributed to contamination. Contaminants can be organic or inorganic particles, films or molecular compounds, ionic materials or atomic species. Examples of ionic contaminants are sodium, potassium, lithium, calcium, boron, manganese, sodium, titanium, zirconium, aluminum, sulfur and magnesium. Other damaging elemental impurities include heavy metals, for example, such as iron, copper, nickel and gold.
Particularly problematic, however, are analytes, such as high valence metallic ions, e.g., zirconium (Zr+4), found in planarization fluid compositions and used during planarization of wafers. Although such fluid compositions are generally quite pure, they are, however, not free of contaminants such as the ionic contaminants listed above. These analytes can destabilize a planarization composition in even minute concentrations (ppm or ppb level). The destabilization of the slurry from the presence of these analytes can result in aggregate particles having sufficient size and mass to cause wafer defects, e.g., scratches.
During planarization, typically a rotating substrate of semiconductor material is held against a wetted planarization or polishing surface using a liquid slurry (e.g., a colloidal suspension of abrasive particles) under controlled pressure and temperature conditions. The fluid typically includes an abrasive component, such as alumina, silica, or similar particulates, although, alternatively, a pad could include the abrasive component. During planarization, abrasive particles and contaminants such as high valence ions are generally present at the surface of the substrate being planarized.
Planarization is used to produce a surface with a desired thickness and/or uniformity. However, typical slurries used in the planarization process contain certain levels of metal ions, particularly high valence metal ions. Further, such metal ions, particularly high valence metal ions, destabilize the colloidal suspension of abrasive particles leading to aggregation of such abrasive particles. Such aggregation leads to wafer detects, e.g., scratches, during the planarization of wafers.
The presence of such metal contaminants during wafer processing has become particularly problematic in high density, integrated circuit technology. For example, wafer defects caused by contaminants can cause a device to fail because of improperly defined patterns caused by the defects, by creating unpredictable surface topography, by inducing leakage currents through insulating layers, or by accelerating device wearout.
It has been reported that certain chelating agents have been added to cleaning solutions commonly used to remove particles and organic contaminants on silicon surfaces. Such chelating agents tend to reduce certain metallic contamination deposition on a silicon wafer. However, such wet cleaning procedures are performed after CMP processing and ion contamination and wafer defects such as caused by abrasive particle aggregation may have already caused significant problems to the wafer during the planarization process.
Also, it has been demonstrated that water soluble multidentate chelating agents, particularly water soluble bidentate ionic chelating agents, such as 1,2-ethylenediphosphonic acid (EDP), can be used during planarization processing to remove metal ion contaminants, as disclosed in U.S. patent application Ser. No. 08/682,308, filed on Jul. 17, 1996, entitled xe2x80x9cA Planarization Fluid Composition Including Chelating Agents and Planarization Method Using Same.xe2x80x9d
Thus, improvements in the fluid compositions employed in planarization processes are needed to reduce wafer defects. The present invention, as described below, provides such improvements and overcomes the problems described above and those problems that will become apparent to one skilled in the art from the detailed description below.
The present invention provides fluid compositions for use in the planarization of a substrate surface, such as a wafer. The fluid compositions include a planarization slurry that has an abrasive component and a chemically interactive component that interacts with the surface of the wafer during planarization. The fluid compositions also include an effective amount of at least one crown ether that is capable of isolating at least one charged ion contaminant specie in the planarization slurry.
Charged ion contaminant species that can be isolated using the fluid compositions of the invention include, but are not limited to, ions having valences of +2, +3, +4 or more. Preferably, the charged ion contaminant is a Zr+4ion. Typically, the crown ethers employed in the invention to isolate one or more charged ion contaminants are of the formula benzo or dibenzo-3n-crown-n, where n is a positive whole integer. However, other crown ethers known in the art are also useful in the invention.
Preferably, the fluid composition employed to planarize the surface of a wafer, contains a planarization slurry that has an abrasive component and a chemically interactive component and an effective amount of at least one crown ether, such as dibenzo-14- crown-4 ether, benzo-15-crown-5 ether, dibenzo-18-crown-6 ether or benzo-21 -crown-7 ether or a combination thereof. The crown ether or combination thereof is utilized to isolate at least one ion contaminant specie in the planarization slurry.
A planarization method of the present invention includes providing a wafer and a pad that has contact with the wafer surface, then planarizing the wafer surface using the pad and a fluid composition. The fluid composition contains a planarization slurry that has an abrasive component, a chemically interactive component, and an effective amount of at least one crown ether that is capable of isolating at least one charged ion contaminant specie in the planarization slurry.
The fluid composition used in the planarization method is capable of removing or isolating charged ion contaminant species and include, but are not limited to, ions having valences of +2, +3, +4 or more. Preferably, the charged ion contaminant is a Zr+4ion. Typically, the crown ethers employed in the method can isolate and/or remove one or more charged ion contaminants and are of the formula benzo or dibenzo-3n-crown-n, where n is a positive whole integer. However, other crown ethers known in the art are also useful in the method.
Also provided, is a method for removing charged ion contaminant species from a planarization slurry, and includes combining an aqueous planarization slurry with at least one crown ether in an organic solvent to form a mixture. At least one charged ion contaminant specie can then be isolated from the slurry by separating the organic solvent layer from the aqueous layer to yield a planarization slurry that has a reduced concentration of the at least one charged ion contaminant specie.
The present invention also provides an isolation method. The method includes forming a shallow trench isolation structure that has an oxide surface and a planarization stop layer formed of silicon nitride. The oxide surface is planarized using a fluid composition that contains a planarization slurry that has an abrasive component and a chemically interactive component. The fluid composition also contains an effective amount of at least one crown ether that is capable of isolating at least one charged ion contaminant specie.
In a preferred isolation method, the fluid composition, which contains an abrasive component and a chemically interactive component, has a Zr+4 content of less than 1 ppm, and the planarization process is effectively stopped on a stop layer formed of silicon nitride.